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Drop compression ratio for Turbo

946 Views 31 Replies 9 Participants Last post by  Funkycheeze
Hi all!

I have a 2zz Spyder that needs a headgasket replacement and I intend to go turbo before the summer.
Heres my thinking and I would like someone to correct me if I am wrong.

Cause the high compression ratio on the 2zz stock is 11.5:1 it cannot take much more than 8psi.
So to gain more power (into the 300s) reliably i've read you need to drop compression ratio.
So what I thought I needed to do was get myself mahle forged pistons 10.5:1 as it's in the range from 5-15 psi that i am looking for.
However I saw that cometic has a headgasket that is 1.3mm thick (stock is 0.5mm) and drops compression by one full point (from 11.5:1 to 10.5:1) according to MWR. Which is significantly cheaper and does exactly the same as forged pistons.

Link to both items:
Cometic head gasket – Toyota 2ZZ-GE 82.0-82.5mm 0.052″ (1.3mm) | Monkeywrench Racing
Mahle Piston Set – Toyota 2zz – 10.5:1 compression 82mm | Monkeywrench Racing

Am I being dumb or will this actually work?
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If you need to replace the head gasket anyway, just go with the thicker one and drop the compression. You won't miss the extra point of compression and you'll have more headroom to tune it after the turbo install. This isn't a racecar so no reason to run it on the ragged edge unless you're prepared to deal with the consequences.
Will the lack of compression reduce horsepower by a large margin?
You'll lose around 5hp from the drop in compression. Which will of course be negated when you boost the motor.
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